This invention relates to back pressure-dependent correction of the air/fuel ratio of a mixture being supplied to an internal combustion engine, and a device for practicing the same method.
A fuel supply control system adapted for use with an internal combustion engine, particularly a gasoline engine has been proposed e.g. by U.S. Pat. No. 3,483,851, which is adapted to determine the valve opening period of a fuel injection device for control of the fuel injection quantity, i.e. the air/fuel ratio of an air/fuel mixture being supplied to the engine, by first determining a basic value of the above valve opening period as a function of engine rpm and intake pipe absolute pressure and then adding to and/or multiplying same by constants and/or coefficients being functions of engine rpm, intake pipe absolute pressure, engine temperature, throttle valve opening, exhaust gas ingredient concentration (oxygen concentration), etc., by electronic computing means.
The quantity of air being sucked into engine cylinders can vary with changes in the pressure in the exhaust pipe of the engine, that is, the back pressure, even when other factors for the operating condition of the engine remain unchanged. Therefore, it is desirable to correct the quantity of fuel being supplied to the engine in dependence upon changes in the back pressure in order to achieve an optimum air/fuel ratio.
A change in the back pressure can be caused by a change in atmospheric pressure, which is particularly conspicuous during engine operation at a high altitude. Besides the atmospheric pressure, in an engine equipped with a turbocharger or a like device in particular, the back pressure can largely vary according to changes in the operating condition of the engine. A further factor for the change of the back pressure is a change in the performance of the turbocharger or the like device.
In a conventional fuel supply control system of the above-mentioned kind, it is generally employed to correct the fuel supply quantity for the engine in response to changes in the atmospheric pressure or changes in the exhaust pipe pressure so as to obtain an air/fuel ratio suitable for the engine operation, for improvements in the fuel consumption, emission characteristics and driveability of the engine.
For instance, in a fuel supply control system adapted for correction of the basic valve opening period of a fuel injection valve by means of a correction coefficient as mentioned above, an atmospheric pressure-dependent correction coefficient or a back pressure-dependent correction coefficient is provided as one of the aforementioned correction coefficients, for correction of the air/fuel ratio of the mixture.
However, according to such conventional back pressure-dependent correction of the air/fuel ratio which is determined by intake pipe absolute pressure as noted above, the air/fuel ratio is corrected in dependence upon either the atmospheric pressure or the back pressure alone. That is, the correction amount is not based upon the actual operating condition of the engine per se, making it difficult to perform the air/fuel ratio correction in a perfect manner.